Genome-Wide Analysis of the Peroxidase Gene Family and Verification of Lignin Synthesis-Related Genes in Watermelon

Watermelon (Citrullus lanatus) is an important horticultural crop worldwide, but peel cracking caused by peel hardness severely decreases its quality. Lignification is one of the important functions of class III peroxidase (PRX), and its accumulation in the plant cell wall leads to cell thickening and wood hardening. For in-depth physiological and genetical understanding, we studied the relationship between peel hardness and lignin accumulation and the role of PRXs affecting peel lignin biosynthesis using genome-wide bioinformatics analysis. The obtained results showed that lignin accumulation gradually increased to form the peel stone cell structure, and tissue lignification led to peel hardness. A total of 79 ClPRXs (class III) were identified using bioinformatics analysis, which were widely distributed on 11 chromosomes. The constructed phylogenetics indicated that ClPRXs were divided into seven groups and eleven subclasses, and gene members of each group had highly conserved intron structures. Repeated pattern analysis showed that deletion and replication events occurred during the process of ClPRX amplification. However, in the whole-protein sequence alignment analysis, high homology was not observed, although all contained four conserved functional sites. Repeated pattern analysis showed that deletion and replication events occurred during ClPRXs’ amplification process. The prediction of the promoter cis-acting element and qRT-PCR analysis in four tissues (leaf, petiole, stem, and peel) showed different expression patterns for tissue specificity, abiotic stress, and hormone response by providing a genetic basis of the ClPRX gene family involved in a variety of physiological processes in plants. To our knowledge, we for the first time report the key roles of two ClPRXs in watermelon peel lignin synthesis. In conclusion, the extensive data collected in this study can be used for additional functional analysis of ClPRXs in watermelon growth and development and hormone and abiotic stress response.

Genome-Wide Identification and Characterization of GhCOMT Gene Family during Fiber Development and Verticillium Wilt Resistance in Cotton

Caffeic acid O-methyltransferases (COMTs) play an essential role in lignin synthesis procession, especially in the plant’s phenylalanine metabolic pathway. The content of COMT genes in cotton and the relationship between their expression patterns have not been studied clearly in cotton. In this study, we have identified 190 COMT genes in cotton, which were classified into three groups (I, II and III), and mapped on the cotton chromosomes. In addition, we found that 135 of the 190 COMT genes result from dispersed duplication (DSD) and whole-genome duplication (WGD), indicating that DSD and WGD were the main forces driving COMT gene expansion. The Ka/Ks analysis showed that GhCOMT43 and GhCOMT41 evolved from GaCOMT27 and GrCOMT14 through positive selection. The results of qRT-PCR showed that GhCOMT13, GhCOMT28, GhCOMT39 and GhCOMT55 were related to lignin content during the cotton fiber development. GhCOMT28, GhCOMT39, GhCOMT55, GhCOMT56 and GhCOMT57 responded to Verticillium Wilt (VW) and maybe related to VW resistance through lignin synthesis. Conclusively, this study found that GhCOMTs were highly expressed in the secondary wall thickening stage and VW. These results provide a clue for studying the functions of GhCOMTs in the development of cotton fiber and VW resistance and could lay a foundation for breeding cotton cultivates with higher quantity and high resistance to VW.

Transcriptome provides potential insights into how calcium affects the formation of stone cell in Pyrus

Background The content of stone cells in pears has a great influence on taste. Stone cells are formed by the accumulation of lignin. The treatment of exogenous calcium can affect the lignin synthesis, but this Ca-mediated mechanism is still unclear. In this study, the author performed a comparative transcriptomic analysis of callus of pears (Pyrus x bretschneideri) treated with calcium nitrate Ca (NO3)2 to investigate the role of calcium in lignin synthesis. Results There were 2889 differentially expressed genes (DEGs) detected between the Control and Ca (NO3)2 treatment in total. Among these 2889 DEGs, not only a large number of genes related to Ca single were found, but also many genes were enriched in secondary metabolic pathway, especially in lignin synthesis. Most of them were up-regulated during the development of callus after Ca (NO3)2 treatment. In order to further explore how calcium nitrate treatment affects lignin synthesis, the author screened genes associated with transduction of calcium signal in DEGs, and finally found CAM, CML, CDPK, CBL and CIPK. Then the author identified the PbCML3 in pears and conducted relevant experiments finding the overexpression of PbCML3 would increase the content of pear stone cells, providing potential insights into how Ca treatment enhances the stone cell in pears. Conclusions Our deep analysis reveals the effects of exogenous calcium on calcium signal and lignin biosynthesis pathway. The function of PbCML3 on stone cells formation was verified in pear.

NnLAC17, a Gene Related to Lignin Synthesis, is Involved in Adventitious Root Formation in the Seedlings of Lotus (Nelumbo Nucifera Gaertn)

BarkgroundAdventitious roots (ARs), which are considered as an important member of root system, have an unmatched status in plant growth and metabolism due to the degeneration of primary roots in lotus. The regulation of AR formation was previously revealed and multiple factors were recognized to be involved in this biological process. ResultsIn the present study, we sought to assess the effect of sucrose on AR formation. Based on our results, lignin metabolism, which is regulated by the sucrose signal transduction pathway, is involved in AR development. The lignification degree of the AR primordium was weaker in plants treated with 20 g/L sucrose than in control plants. However, based on the microstructural observation of the AR developmental process, 50 g/L sucrose promoted the lignification process. Lignin content, including monomer and polymer lignin, was determined in the present study. Compared with control plants, the monomer (containing 30%–45% S type and 55%–70% G type) and polymer lignin contents were lower in plants treated with 20 g/L sucrose and higher in plants treated with 50 g/L sucrose. The precursors of monomer lignin were identified in four libraries of differential developmental stages in seedlings using LC-MS/MS technique. The contents of four metabolites, including p-coumaric acid, caffeate, sinapinal aldehyde and ferulic acid for monomer lignin synthsis were lower in the GL50 library than in the GL20 library. Further analysis revealed that the gene expression of these four metabolites had no novel difference in the GL50/GL20 libraries. However, NnLAC17, a gene involved in polymer lignin synthesis, had a higher expression in the GL50 library than in the GL20 library. ConclusionsTherefore, NnLAC17 was cloned, and the overexpression of NnLAC17 was found to directly result in a decrease in AR number in transgenic Arabidopsis plants. These findings suggest that NnLAC17, which is relevant to lignin synthesis, is involved in AR formation in lotus seedlings.

Exogenous Brassinosteroid Facilitates Xylem Development in Pinus massoniana Seedlings

Brassinosteroids (BRs) are known to be essential regulators for wood formation in herbaceous plants and poplar, but their roles in secondary growth and xylem development are still not well-defined, especially in pines. Here, we treated Pinus massoniana seedlings with different concentrations of exogenous BRs, and assayed the effects on plant growth, xylem development, endogenous phytohormone contents and gene expression within stems. Application of exogenous BR resulted in improving development of xylem more than phloem, and promoting xylem development in a dosage-dependent manner in a certain concentration rage. Endogenous hormone determination showed that BR may interact with other phytohormones in regulating xylem development. RNA-seq analysis revealed that some conventional phenylpropanoid biosynthesis- or lignin synthesis-related genes were downregulated, but the lignin content was elevated, suggesting that new lignin synthesis pathways or other cell wall components should be activated by BR treatment in P. massoniana. The results presented here reveal the foundational role of BRs in regulating plant secondary growth, and provide the basis for understanding molecular mechanisms of xylem development in P. massoniana.

Exploring the biosynthetic pathway of lignin in Acorus tatarinowii Schott using de novo leaf and rhizome transcriptome analysis

Acorus tatarinowii Schott is a well-known Chinese traditional herb. Lignin is the major biologically active ingredient and exerts a broad range of pharmacological effects: it is an antitumor, antioxidant, and bacteriostatic agent, and protects the cardiovascular system.In this study, the transcriptomes of the leaf and rhizome tissues of A. tatarinowii Schott were obtained using the BGISEQ-500 platform. 141,777 unigenes were successfully assembled, of which 76,714 were annotated in public databases. Further analysis of the lignin biosynthesis pathway revealed a total of 107 unigenes encoding eight key enzymes, which were involved in the lignin biosynthetic pathway. Furthermore, the expression of the key genes involved in lignin synthesis in different tissues was identified by quantitative real-time PCR. Analysis of the differentially expressed genes showed that most of the upregulated unigenes were enriched in rhizome tissues. In addition, 2,426 unigenes were annotated to the transcriptome factor (TF) family. Moreover, 16 TFs regulating the same key enzyme (peroxidase) were involved in the lignin synthesis pathway. The alignment of peroxidase amino acid sequences and the analysis of the structural characteristics revealed that the key peroxidase enzyme had well-conserved sequences, spatial structures, and active sites. This study is the first to provide comprehensive genetic information on A. tatarinowii Schott at the transcriptional level, and will facilitate our understanding of the lignin biosynthesis pathway.

Integrating transcriptome and proteome analysis to determine the lignin synthesis pathway involved in Panax notoginseng in fungal stress

Background Plants are constantly threatened by various pathogens in a challenging environment. Altemaria panax Whetzel is a destructive pathogen that affects many plants, including Panax notoginseng, and significantly reduces the yield and product quality of Panax notoginseng. It is not clear how Panax notoginseng responds to pathogen infection.Methods Using the advanced advantages of transcriptome and proteomics technology, we studied the response of Panax notoginseng to Altemaria panax stress.Results Compared with the control, fungal infection caused significant changes in the Panax notoginseng transcriptome and proteome. Specifically, a total of 136,100 transcripts and 4,468 proteins were identified. The integration of transcriptome and proteome profiles revealed many candidate transcripts/proteins, which may be involved in lignin synthesis during the activation of defense responses by Panax notoginseng. Many genes and proteins are induced or inhibited by fungi. Among them, the expression levels of genes PAL, 4CL, COMT, CAD and POX in the lignin synthesis pathway are significantly increased, which indicates that the fungus activates the defense response of Panax notoginseng.Conclusions As far as we know, this is the first time that transcriptome and proteome analysis have been combined to study the response of Panax notoginseng to disease. This study provides a wide range of new information about the transcriptome, proteome and their correlation of Panax notoginseng in response to fungal stress. The analysis of this resource allows us to examine the mechanisms of transcription and protein diversification, which expands the knowledge of the complexities of the transcriptome and proteome in traditional Chinese medicines.

Tartary Buckwheat (Fagopyrum tataricum) NAC Transcription Factors FtNAC16 Negatively Regulates of Pod Cracking and Salinity Tolerant in Arabidopsis

The thick and hard fruit shell of Fagopyrum tataricum (F. tataricum) represents a processing bottleneck. At the same time, soil salinization is one of the main problems faced by modern agricultural production. Bioinformatic analysis indicated that the F. tataricum transcription factor FtNAC16 could regulate the hull cracking of F. tataricum, and the function of this transcription factor was verified by genetic transformation of Arabidopsis thaliana (A. thaliana). Phenotypic observations of the wild-type (WT), OE-FtNAC16, nst1/3 and nst1/3-FtNAC16 plant lines confirmed that FtNAC16 negatively regulated pod cracking by downregulating lignin synthesis. Under salt stress, several physiological indicators (POD, GSH, Pro and MDA) were measured, A. thaliana leaves were stained with NBT (Nitroblue Tetrazolium) and DAB (3,3’-diaminobenzidine), and all genes encoding enzymes in the lignin synthesis pathway were analyzed. These experiments confirmed that FtNAC16 increased plant sensitivity by reducing the lignin content or changing the proportions of the lignin monomer. The results of this study may help to elucidate the possible association between changes in lignin monomer synthesis and salt stress and may also contribute to fully understanding the effects of FtNAC16 on plant growth and development, particularly regarding fruit pod cracking and environmental adaptability. In future studies, it may be useful to obtain suitable cracking varieties and salt-tolerant crops through molecular breeding.